Cancer is a leading cause of premature deaths in the developed world. The aim of immunotherapy in cancer is to mount an effective immune response by the body against a tumour. This may be achieved by, for example, breaking tolerance against tumour antigen, augmenting anti-tumor immune responses, and stimulating local cytokine responses at the tumor site. The key effector cell of a long lasting anti-tumor immune response is the activated tumor specific effector T cell. Incomplete activation of effector T cells by, for example, dendritic cells can cause T-cell anergy, which results in an inefficient anti-tumor response, whereas adequate induction by dendritic cells can generate a potent expansion of activated effector T cells, redirecting the immune response towards the tumor.
The cell surface CD40 receptor molecule is a member of the tumour necrosis factor receptor superfamily (TNFR) and is a key regulator in both innate and adaptive immune responses. It is expressed on human antigen presenting cells, in particular B cells, dendritic cells and macrophages, as well as on normal cells, such as fibroblasts, smooth muscle cells, endothelial cells and epithelial cells. Moreover, is it expressed on a wide range of tumor cells including all B-lymphomas, 30-70% of solid tumours, melanomas and carcinomas.
The natural ligand of CD40, designated CD154 or CD40L, is mainly expressed on mature T lymphocytes. CD40L-mediated signalling triggers several biological events, including immune cell activation, proliferation, and production of cytokines and chemokines. Thus, stimulation via the CD40 receptor enhances cellular and immune functions. Its role in cell-mediated immune responses is well known. For example, the activation of dendritic cells via CD40 stimulation, induces activation of effector T cells. Treatment with CD40 agonists may thus provide the means to redirect the immune response and expand effector T cells directed to tumour cells
Antitumour effects have been reported for some anti-CD40 antibodies, with several mechanisms having been identified. An indirect effect is observed for CD40 negative tumors, involving the activation of antigen presenting cells, in particular increased activity by tumor specific cytotoxic T lymphocytes and natural killer cells (NK cells). A direct antitumor mechanism is observed for CD40 positive tumours, wherein the CD40 antibody binding to tumour cells induces cell apoptosis. These mechanisms for anti-tumour activity may be complemented by the stimulation of a humoral response leading to enhanced antibody mediated cellular cytotoxicity (ADCC). However, the systemic administration of anti-CD40 antibodies has also been associated with adverse side effects, such as shock syndrome and cytokine release syndrome.
Accordingly there remains a need for improved cancer therapies, in particular anti-CD40 antibodies suitable for use in therapy.